Changing one's dollars on the black market

Q: I am visiting Argentina for a month. I have come across that the Peso Dollar official rate and black market rate to be very different. The official rate is around 8 pesos while the black market rate is around 15 pesos. Is it permissible for me to change my dollars in the black market? Someone told me that it is not permissible because its a type of riba and cheating and going against the law of the country. Please advise.

Using zakaat money to pay the school fees of poor children

Q: At our school we want to ensure that all zakaats collected on behalf of Zakaat eligible learners is carried out according to Shariah. Could you please provide guidelines for accepting zakaat and using the same for payment of school fees. We also require guidance with formulating a formal appointment letter to collect zakaat for learners eligible to receive zakaat.